1. Field of the Invention
The present invention relates to a fuel injection device, a fuel injection control device, and a control method of the fuel injection device capable of properly performing opening/closing operations of a fuel injection valve including a solenoid and a magnetostrictive element.
2. Description of the Related Art
There has been known a magnet-type fuel injection device used for an internal combustion engine, the fuel injection device including an injector having a fuel injection valve driven by a magnet, a driving power source, and a drive circuit provided between the power source and the injector, the drive circuit supplying a drive current from the power source to the injector when receiving a fuel injection command (an operation signal). A battery is generally used as the driving power source.
In the injector of the magnet-type fuel injection device, when not performing injection, a needle valve is forced to abut an injection hole by a coil spring, and when performing injection, the needle valve is attracted by the magnet to open the injection hole so that the fuel is injected. However, the problem with the injector of the magnet-type fuel injection device is that the fuel injection valve does not open and close sufficiently quick in response to the operation signal. To solve this problem, there is proposed a fuel injection device in which a piezoelectric element (or an electrostrictive element, or a magnetostrictive element) is attached to a portion of the needle of the injector, and the opening/closing operation of the fuel injection valve is adjusted by an elongation operation of the element (refer to Published patent application No. 2004-316644, paragraphs 0005 to 0026, FIG. 2 and others).
However, according to the above patent document, the piezoelectric element is biased through an electric terminal (not shown), and the piezoelectric element is elongated/contracted by the bias. Also, since it is described in the document that the bias to the piezoelectric element is performed with no relationship with the bias of the electromagnetic operation device, the document fails to give any description on what kind of electrical control circuit or control method should be provided to properly perform the opening/closing operation of the fuel injection valve. Further, the document fails to give out a clear relationship between the piezoelectric element operation and the electromagnetic operation when performing the opening/closing operation of the fuel injection valve control.